Method of preparing lithium soap greases



United States Patent 3,015,624 Patented Jan. 2, 1962 3,015,624 METHOD OF PREPARE G LITHIUM SOAP GREASES William R. Hencke, Groves, and Cecil F. McBurnett and Lloyd F. Bridgett, Port Arthur, Tex., assignors to Texaco Inc., a corporation of Delaware No Drawing. Filed Dec. 22, 1958, Ser. No. 781,944

13 Claims. (Cl. 252-41) This invention relates to an improved method for the manufacture of greases thickened with lithium soaps of hydroxy fatty acid materials.

Lithium soap greases are ordinarily prepared by methods which comprise heating a mixture of lithium soap and lubricating oil comprising all or a portion of the lubricating oil employed in the grease to a temperature above the melting point of the soap for a suificient time to obtain a homogeneous solution of soap in oil, and then cooling the mixture rapidly until a grease consistency is obtained. These methods have the disadvantage of requiring special equipment for obtaining the necessary high temperatures, above about 400 F., and careful control of the conditions during cooling in order to avoid graininess of the product. A more convenient low temperature method, wherein the grease mixture is maintained at a temperaturebelow the melting point of the soap, is described by O. P. Puryear and H. V. Ashburn, in US. 2,450,254-5 and US. 2,450,219-20. This meth- 0d comprises s'aponifying a saponifiable material comprising at least a substantial proportion of a hydroxy fatty acid material in situ in the presence of about an equal Weight of lubricating oil, dehydrating at a higher temperature below the melting point of the soap, and then cooling the grease mixture by addition of cold oil comprising the main portion of the lubricating oil employed in the grease. This method obviates the special equipment required with the high temperature procedures and consistently produces smooth products. However, ith'as the disadvantage of producing lithium base greases in very poor yields, and its use has therefore been restricted almost entirely to the production of high priced specialty greases.

The method of the present invention overcomes the disadvantages of the prior art methods discussed above and produces lithium base greases of excellent quality in yields which are substantially equivalent to those obtained by high temperature methods without the necessity of employing temperatures above the melting point of the soap. This method comprises essentially saponifying a hydroxy fatty acid material in situ in the presence of a relatively large amount of lubricating oil, dehydrating at a higher temperature below the melting point of the soap, adding any additional lubricating oil required to obtain a grease mixture containing at least the major amount of the lubricating oil contained in the finished grease with the avoidance of any substantial cooling during the oil addition, then slowly cooling the grease mixture to 250 F. or lower and finishing in the conventional manner. The saponification mixture employed comprises lubricating oil and saponifiable' material in a ratio which is at least about 3:1 by weight and may be as high as about 16:1 by weight. The method of this invention thus difiers from similar low temperature methods of the prior art which have been employed for the preparation of lithium soap greases in the use of these dilute solutions in the soap formation step and in the avoidance of rapidly cooling a concentrated soap solution by the addition of a large amount of oil at a much lower temperature, both of which are necessary for obtaining the advantages sought.

The greases which are prepared inaccordancewith about 200 F.

this invention comprise a lubricating oil as the chief component and a minor amounn suificient to thicken the lubricating oil to a grease consistency, of a lithium soap of a hydroxy fatty acid material comprising at least about 35 percent by Weight of a hydroxy fatty acid material. Preferably the soap comprises at least a major amount, and most suitably at least about percent by weight of a lithium hydroxy fatty acid soap. The amount of lithium soap may vary from about 2 percent by weight up to about 20 percent by weight of the composition. The greases which are prepared most advantageously by the method of this invention are those containing from about 3 to about 12 percent by weight of the lithium soap.

Suitable soap forming hydroxy fatty acid materials which may be employed in the production of these greases are essentially saturated hydroxy fatty acids containing 12 or more carbon atoms and one or more hydroxyl groups separated from the carboxyl group by at least one carbon atom, the glycerides of such acids and the lower alkyl esters of such acids. Preferably, the acid contains about 16 to about 22 carbon atoms per molecule. Such materials may be obtained from naturally occurring glycerides or produced synthetically by methods such as the hydroxylation of fatty acids or the hydrogenation of ricinoleic acid or castor oil. Particularly suitable materials of this character are 12-hydroxys-tearic acid and the methyl ester thereof, and hydrogenated castor oil. Such hydroxy fatty acid materials may be employed in the saponification in admixture with saponifiable materials of the conventional type, as disclosed, for example, by H. V. Ashburn and O. P. Puryear in US. 2,450,220. The preferred sapouifiable materials of this type are saturated fatty acids containing from about 16 to 24 carbon atoms per molecule and the glycerides of such acids.

The lubricating oils employed in these greases include particularly the conventional mineral lubricating oils, having Saybolt Universal viscosities in the range from about 70 seconds at F. to about 225 seconds at 210 F., and synthetic hydrocarbon oils having viscosities in this range, such as those obtained by cracking and polymerizing products of the Fischer-Tropsch process and the like. The mineral lubricating oils may be either uaphthenic or parafiinic oils, or blends of difierent oils of these types. Other synthetic oleaginous compounds such as polyesters, polyethers, etc. having viscosities with in the lubricating oil viscosity range may also be employed in these greases as at least part of the lubricating oil component. Suitable compounds of this type include particularly the aliphatic dicarboxylic acid diesters, such as, for example, di-Z-ethyl hexyl sebacate, di(secondary amyl) sebacate, di-Z-ethyl hexyl azelate, di-isooctyl adipate, etc. However, a lubricating oil which is substantially unreactive under the saponification conditions is preferably employed in the saponification mixture. Lubricating oils employed for this purpose are preferably mineral oils having viscosities of at least about 300 seconds Saybolt Universal at 100 F., which may be mixtures of lighter and heavier oils.

Various additives of the usual types such as corrosion inhibitors, oxidation inhibitors, extreme pressure agents, antiwear agents, etc., may be employed in these greases. Suitable oxidation inhibitors include particularly those of the amine type, such as, for example, diphenylamine, phenylalphanaphthylamine and tetramethyl diaminodiphenyl methane. Suitable extreme pressure additives include sulfurized fatty oils and lead soaps, which may be employed either separately or in combination.- Such compounds may be added to the grease mixture during cooling, preferably when the grease mixture is below In carrying out the grease preparation, the grease kettle is charged with the saponifiable material and lubricating oil in amounts such as to give an oil-fat ratio of from about 3:1 to about 16:1 by weight, water, and lithium hydroxide in approximately the stoichiometric amount required to react with the saponifiable material. If desired, a small excess of lithium hydroxide may be employed, such as to give a grease containing up to about 0.5 per cent by weight of free lithium hydroxide. The amount of water employed is preferably sufiicient to give about a 2 to 20 percent lithium hydroxide solution. These materials may be introduced into the kettle in any order desired, but it is preferred to first dissolve the lithium hydroxide in water before mixing it with the saponifiable material.

The kettle is then heated, under substantially atmospheric pressure, and the kettle contents gradually brought up to a temperature in the range from about 300 F. to about 10 F. below the melting point of the soap, preferably at a rate such that the dehydration is substantially complete by the time the mixture has reached about 300 F as shown by the cessation of foaming. Ordinarily, this will require at least about four hours, although slower heating may be employed if desired in order to reduce the amount of foaming. The grease mixture is preferably heated at above 300 F. for at least about one-half hour for completion of the dehydration and development of the soap fibers. Additional lubricating oil is added if necessary while the temperature of the grease mixture is maintained above about 300 F. so that the grease mixture before cooling contains at least the major portion of the lubricating oil contained in the finished grease. The grease mixture is then cooled slowly, such as at a rate below about 10 F. per minute, and preferably at a rate below about 5 F. per minute, with continued stirring. The cooling may be carried out by any convenient method, such as by passing cooling fluid through the kettle jacket, but no more than a minor amount of lubricating oil, such as below about 25 percent by weight, and preferably below about percent by weigth, of the total oil contained in the grease, should be added at a lower temperature than the grease mixture during the cooling in order to avoid substantially reducing the grease yield. The grease is finally drawn at a temperature below about 200 F. and finished in the usual manner, ordinarily by milling and with the addition of a small amount of additional lubricating oil if necessary to obtain a grease of the desired grade. The milling is preferably carried out in a manner which involves subjecting the grease to shearing at a rate above about 100,000, and preferably above about 200,000 reciprocal seconds. It is very suitably carried out by passing the grease through a colloid mill, such as a Premier Colloid Mill set at about 0002-0006 inch clearance.

Under the preferred conditions, the saponification mixture comprises lubricating oil and saponifiable material in a weight ratio of from about 4:1 to about 10:1, respectively, and additional lubricating oil is added at above about 300 F. if necessary to give 'a ratio of at least about 8: l, and preferably at least 10:1, respectively, before the grease mixture is cooled to below 300 F. The maximum temperature to which the grease mixture is heated will depend somewhat upon the saponifiable material employed. When 12-.hydroxystearic acid or the methyl ester thereof is employed as the saponifiable material, the most suitable maximum temperature is in the range from about 315 F. to about 350 F. Dilution of the grease mixture at a temperature above about 300 F., is preferably carried out slowly, such as at a rate below about 0.1 pounds of oil added per minute per pound of grease concentrate, and most advantageouslyat a rate below about 0.05 pounds of oil per minute per pound of grease concentrate.

The following examples are given for the purpose of further disclosing the invention.

EXAMPLE I A grease comprising essentially a mineral lubricating 4 oil thickened with 7.0 percent by weight of lithium 12- hydroxystearate was prepared by the method of this invention employing lubricating oil and saponifiable material in a ratio of about 7:1 respectively in the saponification mixture, and adding the remainder of the lubricating oil to the grease mLxture while it was maintained at a temperature above 300 F.

The mineral oil employed in the grease was a blend in about 2. 942100 ratio by weight respectively of a refined wax distillate oil having a viscosity index of about and a Saybolt Universal viscosity of about 180 seconds at F., and a refined residual oil having a viscosity index of about 80 and a Saybolt Universal viscosity of about seconds at 210 F., obtained by furfural refining, clay and acid treating, and'dewaxing a residual oil from a mixed base crude.

The saponifiable material employed was a commercial l2-hydroxystearic acid, having a saponification number of 187 and a neutralization number of 176.

Following is a detailed description of the method employed in the greasepreparation. A 300 pound capacity jacketed Dowtherm heated and cooled open kettle was charged with 3.99 pounds of lithium hydroxide monohydrate and 20 pounds of water and the mixture heated to about 105 F. with stirring. When the lithium hydroxide monohydrate was dissolved, 20.6 pounds of 12- hydroxystearic acid and 141.4 pounds of refined residual oil were added and the mixture heated to 300 F. in about 5 /2 hours with continued stirring. The mixture was then heated further and the temperature maintained at about 325 F. for about 2 /3 hours While 132.9 pounds of refined distillate oil were added gradually. The heat was then cut and the grease mixture cooled to about 200 F. in 40 minutes. When the grease mixture was below about 200 F. 1.5 pounds of diphenylamine and 3.0 pounds of a commercial inhibitor consisting of a mixture of aliphatic diamines, having the formula where R is an alkyl group derived from tallow, were added. The grease was finally drawn at F. and milled in a laboratory model Premier colloid mill at 20.0 pounds inlet pressure and 0.003 inch clearance. A smooth grease of excellent texture and appearance was obtained, having an ASTM worked penetration at 77 F. of 351.

The following table shows the results obtained in the above preparation comparatively with those obtained by employing a low temperature method of the prior art. Grease No. l of the table was obtained as described above. Grease No. 2 was prepared employing the same materials and in the same manner except as otherwise indicated in the table. The penetration data in each case were obtained upon the milled product.

Table I Grease No 1 2 Soap content, percent 011: fat ratio of charge. Top temperature, F,

vart teachings was obtained by employing a very dilute saponification mixture and by adding the remainder of the lubricating oil to the grease mixture while it was maintained at a temperature above 300 F.

EXAMPLE II Another grease was prepared in accordance with this invention employing hydrogenated castor oil as the saponifiable material. This material had a saponification number of 180, a neutralization number of 3, an iodine number of 3 and a hydroxyl number of 155. The lubricating oils employed were as described in Example I. The other conditions employed in the grease preparation were substantially the same as those employed in Example I, except that the grease was heated to a maximum tem perature of 340 F., and in addition to the amine oxidation inhibitors, 8 percent of an extreme pressure additive, consisting of 15 percent by weight of lead naphthenate prepared from naphthenic acid having a molecular weight of 223 and 85 percent by weight of sulfurized sperm oil, was added to the grease mixture at a temperature below 200 F. during cooling. A smooth 6.5 soap content grease was obtained having an ASTM worked penetration at 77 F. of 285 and good extreme pressure properties.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made Without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. The process of preparing a lubricating grease comprising as the major component a lubricating oil thickened to a grease consistency by a lithium soap which comprises providing a saponification mixture consisting essentially of a substantially saturated saponifiable material comprising at least about 35 percent by weight of a soapforming hydroxy fatty acid material, a basic lithium compound in an amount corresponding approximately to the stoichiometric amount required to react with the said saponifiable material, a minor amount of water, and a lubricating oil which is substantially non-reactive under the saponification conditions in an amount equal to from about 3 to about 16 times the weight of the said saponifiable material, heating the said mixture under substantially atmospheric pressure gradually up to about 300 F. over a period of time suflicient to obtain complete saponification, further heating the resulting saponified mass up to a maximum temperature in the range from about 300 F. to about F. below the melting point of said soap for a suflicient time to accomplish dehydration, adding any additional lubricating oil required to obtain a grease mixture containing at least the major amount of the lubricating oil contained in the finished grease with the avoidance of any substantial amount of cooling and while the grease mixture is maintained at a temperature of at least about 300 F., and thereafter cooling the said grease mixture to the drawing temperature at a rate below about 10 F. per minute.

2. The process according to claim 1 wherein the saponifiable material comprises at least a major portion of a hydroxy fatty acid material.

3. The process according to claim 1 wherein the said saponifiable hydroxy fatty acid material is chosen from the class consisting of l2-hydroxystearic acid and the esters thereof.

4. The process according to claim 1 wherein the said hydroxy fatty acid material is hydrogenated castor oil.

5. The process according to claim 1 wherein the said hydroxy fatty acid material is 12-hydroxystearic acid.

6. The process according to claim 1 wherein the said hydroxy fatty acid material is the methyl ester of 12 hydroxystearic acid.

7. The process according to claim 1 wherein the said lubricating oil is a mineral lubricating oil.

8. The process according to claim 1 wherein the ratio of lubricating oil to saponifiable material employed in the saponification mixture is within the range from about 4:1 to about 10:1 by weight.

9. The process according to claim 1 wherein the grease mixture comprises lubricating oil and soap in a ratio of at least about 8:1 by weight before it is cooled below 300 F.

10. The process according to claim 1 wherein the grease mixture is finished by milling.

11. The process of preparing a lubricating grease comprising as the major component a mineral lubricating oil thickened to a grease consistency by about 3-12 percent by weight of lithium hydroxy fatty acid soap which comprises providing a saponification mixture consisting essentially of a hydroxy fatty acid material selected from the class consisting of l2-hydroxystearic acid and esters thereof, lithium hydroxide in an amount corresponding approximately to the stoichiometric amount required to react with the said hydroxy fatty acid material, a minor amount of water, and a mineral lubricating oil in an amount equivalent to between about 4 and about 10 times the weight of the said hydroxy fatty acid material, heating the said mixture gradually under substantially atmospheric pressure up to about 300 F. over a period of time sufficient to obtain complete saponification, further heating the resulting saponified mass up to a temperature in the range 300 F.350 F. for a sufficient time to accomplish dehydration, adding any additional lubricating oil required to obtain a grease mixture containing at least about percent by weight of the amount of lubricating oil contained in the finished grease while the grease mixture is maintained at a temperature above about 300 F. thereafter cooling the said grease mixture to about 200 F. at a rate below about 5 F. per minute and drawing.

12. The process according to claim 11 wherein the said grease mixture before cooling to below about 300 F. comprises lubricating oil and soap in a weight ratio of at least about 10:1

13. The process according to claim 11 wherein the said grease is finished by milling.

References Cited in the file of this patent UNITED STATES PATENTS 2,652,366 Jones et al Sept. 15, 1953 

1. THE PROCES OF PREPARING A LUBRICATING GREASE COMPRISING AS THE MAJOR COMPONENT A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY BY A LITHIUM SOAP WHICH COMPRISES PROVIDING A SAPONIFICATION MIXTURE CONSISTING ESSENTIALLY OF A SUBSTANTIALLY SATURATED SAPONIFIABLE MATERIAL COMPRISING AT LEAST ABOUT 35 PERCENT BY WEIGHT OF A SOAPFORMING HYDROXY FATTY ACID MATERIAL, A BASIC LITHIUM COMPOUND IN AN AMOUNT CORRESPONDING APPROXIMATELY TO THE STOICHIOMETRIC AMOUNT REQUIRED TO REACT WITH THE SAID SAPONIFIABLE MATERIAL, A MINOR AMOUNT OF WATER, AND A LUBRICATING OIL WHICH IS SUBSTANTIALLY NON-REACTIVE UNDER THE SAPONIFICATION CONDITIONS IN AN AMOUNT EQUAL TO FROM ABOUT 3 TO ABOUT 16 TIMES THE WEIGHT OF THE SAID SAPONIFIABLE MATERIAL, HEATING THE SAID MIXTURE UNDER SUBSTANTIALLY ATMOSPHERIC PRESSURE GRADUALLY UP TO ABOUT 300* F. OVER A PERIOD OF TIME SUFFICIENT TO OBTAIN COMPLETE SAPONIFICATION, FURTHER HEATING THE RESULTING SAPONIFIED, MASS UP TO A MAXIMUM TEMPERATURE IN THE RANGE FROM ABOUT 300* F. TO ABOUT 10* F. BELOW THE MELTING POINT OF SIAD SOAP FOR A SUFFICIENT TIME TO ACCOMPLISH DEHYDRATION, ADDING ANY ADDITIONAL LUBRICATING OIL REQUIRED TO OBTAIN A GREASE MIXTURE CONTAINING AT LEAST THE MAJOR AMOUNT OF THE LUBRICATING OIL CONTAINED IN THE FINISHED GREASE WITH THE AVOIDANCE OF ANY SUBSTANTIAL AMOUNT OF COOLING AND WHILE THE GREASE MIXTURE IS MAINTAINED AT A TEMPERATURE OF AT LEAST ABOUT 300* F., AND THEREAFTER COOLING THE SAID GREASE MIXTURE TO THE DRAWING TEMPERATURE AT A RATE BELOW ABOUT 10* F. PER MINUTE. 